Photovoltaic power generation that converts solar light energy directly to electricity is well known, however in recent years there has been increased focus on solar heat-utilizing systems that first convert solar light energy to heat, and then utilize the heat for electric power generation. In such solar heat-utilizing systems, sunlight is collected with a collector and the collected sunlight is used to heat a heating medium (such as oil, dissolved salts or molten sodium) in a container or flow channel. Provision of covering materials, thin-films and the like on the surfaces of containers or flow channels is also being studied as a way of accelerating heating of the heating medium by the collected sunlight.
PTL 1, for example, proposes a radiation-selective absorption coating to be used particularly in the absorbing tube of a parabola collector, the coating being composed of an infrared region reflective layer, at least one absorbing layer situated on the reflective layer, and an anti-reflection layer situated on the absorbing layer, the reflective layer being situated on two or more barrier layers, and the second barrier layer of the two or more barrier layers being composed of a SiOx compound.